Inflammation in many settings appears to be mediated by and/or amplified by phospholipase. This investigator and his colleagues have shown enhanced phospholipase A2 enzyme activities in cells and synovial fluid from patients with rheumatoid arthritis. They have also discovered and characterized a phospholipase A2 activating protein (PLAP) and have demonstrated the consequences of this protein on cells and phospholipase A2. They have shown that injection of PLAP into rabbit joints has resulted in an inflammatory arthritis response which closely resembles rheumatoid arthritis. In addition, exposure of peripheral blood leukocytes to PLAP has resulted in an eicosanoid and superoxide generation along with cellular degranulation. They have recently cloned and obtained the cDNA for PLAP. They also have generated preliminary evidence for a mechanism of action for phospholipase A2 activation that represents an alternative to an increase in intracellular calcium concentration. In this fourth submission of this project, previously judged in December 1993 to have been on the cusp of outstanding by this committee, the investigator proposes to continue these studies. Under the first specific aim, they will express PLAP in vitro, purify PLAP in quantity, characterize the purified protein, and obtain amino acid sequences. Under the second specific aim, the investigators will clone PLAP from a human cDNA source. They will evaluate the genetic regulation of PLAP production by inflammatory stimuli and as a new component of this specific aim, they will characterize the activity of PLAP in an animal model of PLAP-induced rheumatoid arthritis.